docs: def file_chunk(filename, size=_BUFFERING):
      """
      returns a generator function which when called will emit x-sized
      chunks of filename's contents
      """
  
      def chunks():
          with open(filename, "rb", _BUFFERING) as fd:
              buf = fd.read(size)
              while buf:
                  yield buf
                  buf = fd.read(size)
      return chunks